Widely known in the art is an axial fan having an electric motor with a shaft carrying a vane impeller. The fan is provided with a special device for regularly rotating the fan casing. During operation this fan generates a perceptible aerodynamic noise which is caused by separation of flow moving around the vanes of the rotating impeller which is characteristic of all air blowing machines of the vane type. The vanes of the operating fan can also be a cause of injuries due to a careless approach to the fan impeller.
In addition, the fan can create a directional turbulent flow in one direction, i.e. the fan has a predetermined limited space coverage which can only insignificantly be enlarged by regularly rotating the electric motor casing. The directional character of the turbulent flow results in overcooling of certain areas of a human body which is within the closest range of the fan.
Most similar to the invention is a fan (PCT/SU 88/00025), comprising a casing having walls defining a flow duct. The flow duct accommodates a multiple-disc rotor in the form of a plurality of coaxial discs connected to one another in spaced relation to each other. The rotor is connected to a drive shaft, e.g. to an electric motor shaft and is mounted for rotation about its axis. In addition, baffles provided in the flow duct are positioned on the two opposite sides of the rotor to extend along the axis thereof. The baffles define suction and delivery areas with the casing walls. This fan, owing to viscous friction forces in the boundary zones adjacent to the surfaces of the discs of the rotating rotor generates two oppositely directed air streams. The absence of large-scale separated and vortical flows in the working zone which are characteristic of vane-type machines in such a fan ensures a low level of aerodynamic noise generated by the fan. The fan construction ensures a closed accommodation of the impeller so as to rule out any inadvertent touching of the discs and the rotating rotor. The character of energy transmission to the air in such a fan causes generation of outlet streams in the laminary mode within a large range of rotor speeds owing to low hydraulic diameters of flow passages which are in the form of narrow slits between the adjacent discs. Laminary air flows can somewhat lower the level of overcooling of parts of a human body within the range of the fan and reduce the incidence of colds. In addition, the provision of two pairs of suction and delivery areas which are located adjacent to each other and positioned on opposite sides of the rotor in the casing reduces the directional character of the escaping streams owing to air overflow from the delivery areas into the adjacent suction areas thus contributing to a diffusion of flow and a decrease in harmful action upon a human body.
However, a strict flow of two parallel air streams in the opposite direction, with the cross-sectional size of the streams being about equal to the size of passages of the flow duct, results in directed streams so that comfort conditions for a human being in a room that would feature a moderate air exchange distributed over the whole room space cannot be provided to ensure a favourable and safe environment for a human being, especially at high temperature and humidity.